Itthi Trisirisatayawong a,⁎, Marc Naeije b, Wim Simons b, Luciana Fenoglio-Marc c
a Department of Survey Engineering, Chulalongkorn University, Bangkok, Thailand
b Delft Institute of Earth Observation and Space Systems, Delft University of Technology, Delft, Netherlands
c Institut für Physikalische Geodäsie, Technische Universität Darmstadt, Darmstadt, Germany
a b s t r a c t
Investigation of long-term tidal data and short-term altimetry measurements reveals that sea level in the Gulf of Thailand is rising significantly faster than global average rates. Upward land motion detected from repeated precise GPS campaign measurements is used to correct the apparent sea level change from tide gauge, yielding absolute long-term trends as follows: Sattahip (1942–2004) 5.0±1.3 mm/yr, Ko Sichang (1940–1999) 4.5±1.3 mm/yr and Ko Mattaphon (1964–2004) 4.4±1.1 mm/yr. Dual-crossover minimization of multi-mission altimetry data covering the 1993–2009 period reveals the following absolute sea level rates: Sattahip 4.8±0.7 mm/yr, Ko Sichang 5.8±0.8 mm/yr, Ko Lak 3.6±0.7 mm/yr and Ko Mattaphon 3.2± 0.7 mm/yr. In other parts of the Gulf, the 1993–2009 rising rates are also in the range of 3 to 5.5 mm/yr. In the entire Gulf we don't find any evidence of sea level falling. At Ko Lak where the collocation of Topex-class altimetry ground track and the tidal station is extremely good, vertical land motion derived from the difference of sea level change rates detected by altimetry and tidal data is used to correct the apparent rate, yielding an absolute long-term (1940–2004) rate of 3.0±1.5 mm/yr. The differences between the altimetrybased rates and the absolute tide gauge sea level trends can be explained by interannual variations like ENSO and decadal variations due to solar activity and lunar nutation. Post-2004 tidal data have been treated separately in our study because reliable values of region-wide vertical co-seismic displacements and postseismic velocities caused by the 2004 Mw9.2 Sumatra-Andaman earthquake are still not accurately known. Exclusion of these data will not significantly change the determined long-term absolute sea level change rates because of the relatively short time span of post-earthquake sea level data compared to the complete tidal record. The impact of fast rising sea level combined with high rates of post-seismic downward crustal motions as indicated by GPS data makes coastal areas and river estuaries along the Gulf of Thailand highly vulnerableto flooding, particularly the low-lying city of Bangkok.
การศึกษาระดับน้ำทะเลในช่วงระยะยาวและความสูงของระดับน้ำทะเลในช่วงระยะสั้นโดยใช้เทคนิค GPS พบว่าระดับน้ำทะเลในอ่าวไทยมีอัตราการเพิ่มสูงขึ้นมากกว่าอัตราเฉลี่ยในระดับโลก ดังนั้นจึงส่งผลกระทบให้บริเวณพื้นที่ชายฝั่งและปากแม่น้ำของอ่าวไทยมีความล่อแหลมที่จะเป็นบริเวณที่โดนน้ำท่วม โดยเฉพาะในพื้นที่กรุงเทพฯ
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